Ground strap assembly



Oct. 27, 1970 L. J. TORDOFF 3,537,060

I GROUND STRAP ASSEMBLY Filed Jan. 8, 1969 INVENTOR. ZmamJ TOEDOFF JM/Mfdg M United States Patent US. Cl. 339-14 4 Claims ABSTRACT OF THE DISCLOSURE An easily applied constant-tension ground strap assembly having particular utility in the grounding of power cable shields at cable terminations.

This invention relates to clamping bands or straps for making permanent electrical connection to articles such as rods, pipes and cables, and having particular utility in the grounding of power cable shielding at cable termination or splice areas.

An easily applied metal strap member for making electrical connection to cable shields is described in Hervig US. Pat. No. 3,324,234. Resilient point or line contact is obtained with angularly disposed spring contact arms. The pressure which can be exerted by such arms is limited.

Another form of strap member, described in Heller US. Pat. No. 3,189,961, is provided with a number of bends or transverse corrugations designed to supply additional spring tension, necessitated in part by the relaxation of tension during the closing or locking action, and requiring that a relatively stiff strap be used.

The strap assembly of the present invention is sufiiciently thin and soft to be easily applied by hand under tension suificient to provide fully conductive contact with the cable shield. The assembly conforms closely to the shield surface and takes up a minimum of space in the completed termination assembly. Tension fully adequate to provide the required contact and positioning is permanently maintained.

In the drawing, FIG. 1 is a plan view and FIG. 2 an edge elevation of a preferred form of the ground strap assembly, and FIG. 3 is a partial elevation showing the assembly applied to a power cable.

The assembly comprises a thin flexible soft metal strap having a wider first end portion 11 and an elongate narrower opposite end portion 12. The wider end is narrowly transversely slotted to provide a slot 13 through which the end 12 may be slidably inserted.

A central portion 14, here shown to be a continuation of the wider first end portion, is centrally longitudinally slotted to provide a slot 15 defined in part by narrow side edge members 16, 17 which as shown in FIG. 2 are outwardly bowed. The strip is perforated adjacent each end of the slot 15 to provide perforations 18, 19 through which are inserted the ends of a tension coil spring 20, shown in substantially relaxed position. The spring is sutficiently stifl? so that forces applied at opposite ends of the strap by normal hand pulling are just suificient to straighten the bowed edges 16, 17.

A ground wire 21 may be aflixed directly to the outer surface of the wider end portion, e.g. by soldering.

In a specific example the strap is madeof 15 mil flat dead soft tin-plated copper. The wider end and center portions are 4 inch wide and when flattened extend a total of three inches in length. The tongue-like narrow end is inch wide and five inches in length. The slot 13 is V 2 inch long, inch wide, and is centered 1% inches from 3,537,060 Patented Oct. 27, 1970 the end of the strap. The slot 15 is inch x inch, the two side edge strips 16, 17 thus being each inch in width. The ground connection wire is soldered to the strap at about inch from the end, thus avoiding interference during application of the assembly.

FIG. 3 illustrates the application of the assembly of FIGS. 1 and 2 in a typical power cable termination. The cable 22 is first prepared to expose the center conductor, a portion of the inner insulation, and a short terminal section of the conductive ground or shielding layer. The ground strap assembly 10 is then wrapped around the exposed portion of the shielding layer and the tongue 12 passed through the slot 13. The strap is next pulled taut to extend the spring 20 and substantially eliminate the bow in the edges 16, 17; and the tongue is then bent back over the edge of the slot 13 to retain the assembly in extended condition. Surplus length of the tongue 12 may then be removed, leaving but a short folded segment 23. The ground connection wire 21 is extended beyond the close-fitting cap 24 which supports an outer insulating sleeve, not shown, and which is subsequently to be filled with self-hardening encapsulating resin composition. The free end of the wire 21 is available for connection to ground. The portion of the insulated conductor extending past the strap assembly is desirably first wrapped with stress control tape 25; or a stress control cone may less conveniently be used. The sleeve and resin are then applied.

The invention will therefore be seen to provide a ground strap assembly which is soft and flexible for easy application and eifective conformability, requires a minimum of space, can be applied without tools, yet provides and maintains fully conductive pressure-contact with the surface to which applied.

What is claimed is as follows:

1. A flexible clamp assembly comprising an elongate thin flexible soft metal strap having a transversely slotted wider first end portion and an extended foldable narrower opposite end portion slidably insertable through the slot in said first end, and a centrally longitudinally slotted central portion; and tension spring means extending along the slot in said central portion for urging said end portions toward said central portion.

2. The assembly of claim 1 wherein said strap is perforate to provide perforations adjacent the ends of the slot in the central portion and said spring means is a coil spring the ends of which are retained in said perforations.

3. The assembly of claim 2 wherein said spring is in relaxed position and the side strips of the central portion defining the side edges of the slot therein are outwardly bowed, and wherein said spring is of suflicient strength to permit extension under normal hand pulling only to the extent necessary to straighten said bowed edges.

4. The assembly of claim 1 including a ground-wire connection at said first end portion.

References Cited UNITED STATES PATENTS 580,199 4/1897 Sommerfeld 24-20 1,827,243 10/1931 Kuehner 24-71 2,467,006 4/1949 Bliss 24-70 3,189,961 6/1965 Heller 24-20 3,324,234 6/1967 Hervig 24-20 JAMES A. LEPPINK, Primary Examiner US. Cl. X.R. 

